The county coroner's office said Saturday it appears the woman, Jessica Erickson of Fernley, Nev., had a heart condition and died of natural causes.

Like several other high-speed rides such as Big Thunder and Space Mountain, Disneyland alerts guests to their possible hazards before boarding. A sign at the entrance to the "turbulent flume ride" warns: "Guests must be in good health, free from back, heart or neck problems, motion sickness or any other condition that could be aggravated by this attraction."

Erickson was visiting relatives in the Riverside area, according to the coroner's office. About 10:45 p.m., Erickson raced down the ride's finale--a five-story plunge where patrons get their pictures snapped, often while raising their arms over their heads and screaming, Disneyland officials said.

"As the log pulled into the load/unload area, cast members noticed she appeared ill," said Lindsey Schnebly, publicity manager at Disneyland. "They stopped the attraction and she was removed from the ride."

The death marks the first such incident on the popular attraction since it opened in July, 1989, Disneyland officials said.

"This is the first time anything like this has happened" at Splash Mountain, Schnebly said. "This is obviously extremely rare."

Erickson was pronounced dead at 11:32 p.m. at Western Medical Center-Anaheim, according to the coroner's office.

"She was on the ride, but it was a natural death," a coroner's spokeswoman said. "It had nothing to do with the ride and she didn't fall out of the ride."

Added deputy coroner Kurt Murine: "She had some things wrong with her physically, which could very well explain the death. But just to rule out any other factors, we're doing a toxicology screen and some other microscopic tests."

Hundreds of people were lined up for the ride Thursday night when park officials announced they were experiencing technical difficulties and cleared everyone out, said park visitor 37-year-old Timothy Lazuka, of Fountain Valley.

A distraught friend of Erickson's was escorted out by paramedics and Lazuka said he heard her say her friend "was dead."

Disneyland officials inspected the ride and found it was "operating normally" and reopened the attraction within 30 minutes, Schnebly said.